CHARLOTTE, N.C. (AP) — Conservatives have pulled advertising dollars out of Pennsylvania and Michigan and instead are focusing their money on less costly toss-up states.

Independent groups are spending nearly $13 million in the coming days to counter President Barack Obama's nominating convention in hopes of limiting any improvement he might see in polls.

But conservatives' hopes of expanding the playing field for Republican presidential nominee Mitt Romney are on hold for the moment, according to consultants who track spending on political ads.

"Over the last several weeks, the dynamics have been changing in a number of states that have led us to dedicate resources elsewhere," said Jonathan Collegio, a spokesman for American Crossroads, a super PAC advised by George W. Bush political guru Karl Rove.

While he said Pennsylvania remains highly competitive, Collegio said that "a statewide buy in Pennsylvania can cost more than buys in several other states combined."

American Crossroads on Wednesday announced it planned to spend $6.8 million over the next 10 days to air ads criticizing Obama's economic record. The group is running its ad in Colorado, Florida, Iowa, North Carolina, New Hampshire, Nevada, Ohio and Virginia for the next 10 days.

Another conservative independent group, Americans for Prosperity, is spending $6.2 million on ads critical of Democrats' national health care overhaul. Founded by billionaire oil magnate brothers David and Charles Koch, the group is running ads in Colorado, Florida, Iowa, Minnesota, Nevada, New Hampshire, New Mexico, Ohio, Virginia, Wisconsin and North Carolina.

The group's ad, also released Wednesday, is the final piece of a $27 million effort in recent weeks to weaken Obama's re-election prospects.

But Pennsylvania, a state Obama won in 2008 with close to 55 percent of the vote, is not on the schedule for the latest advertising buys. Nor is Michigan, the state Obama won with 57 percent and which Romney's father led as governor — and where Romney was born and raised.

Romney has not advertised in Pennsylvania since April. Obama's last advertising effort was in July.